This invention relates generally to catheter-type apparatus for use in treating a patient and, more particularly, to a radiation treatment system including a radioguide catheter having radiation shielding and a related method of use.
Physicians now use radiation to treat an increasing number of medical problems. One form of radiation treatment involves the insertion of a radioactive source wire, carrying a radiation source, into a patient""s body. The radiation source incorporates a radioactive isotope. Typically, a physician feeds the source wire into the patient""s body through a lumen of an implanted radioguide catheter.
Because different patients require a variety of different radiation treatments, a physician presently needs the availability of a wide selection of radioactive source wires. This selection may include radiation sources having both different lengths and different levels of radioactivity. Furthermore, because radioactive isotopes have limited half-lives, the radiation sources have a limited usage life. Thus, this selection of radioactive source wires, and their radiation sources, needs replacement on a regular basis, at significant expense.
One use of such a radioactive source wire is intravascular radiotherapy (IRT). IRT prevents or controls restenosis following percutaneous transluminal angioplasty (PTA), as described in U.S. Pat. No. 5,199,939. IRT also shows promise in the prevention or long-term control of stenosis following a cardiovascular graft procedure or other trauma to a vessel wall.
A physician performing PTA typically examines an area of a blood vessel suffering from stenosis, and then selects a balloon catheter having a length and diameter commensurate with the length and diameter of the stenosis. The physician threads a guide wire and a guide catheter to the area of stenosis, and then uses the guide wire and guide catheter to guide the balloon catheter to its desired position. Actuated by the physician, the balloon catheter expands the area of stenosis. Finally, the physician removes the balloon catheter, leaving the guide wire and guide catheter in place if another procedure, such as IRT, is to follow.
To perform IRT, the physician selects a radioactive source wire that carries a radiation source commensurate in length and diameter to the expanded area of stenosis. The source wire typically takes the form of a solid nickel-titanium alloy core, and the radiation source takes the form of a radioactive isotope, such as iridium, or Phosphorus-32 embedded within the source wire, at its distal tip. This radiation source must be used with extreme care. Even short exposures at close distances can result in radiation injury.
The source wire is initially stored in a remote afterloader, which includes a heavily shielded storage compartment for shielding the radiation source when the source wire is fully retracted into the afterloader. Changing the source wire is a difficult process, entailing risks of radiation exposure.
The IRT is performed by advancing a flexible, radioguide catheter through the implanted guide catheter and along the implanted guide wire in a patient""s cardiovascular system until the radioguide catheter""s distal end is at or near the vessel region to be treated, e.g., the region previously subjected to the angioplasty procedure. Preferably, the radioguide catheter is radially centered in the vessel region.
After the radioguide catheter has been positioned, the afterloader advances the source wire longitudinally through a lumen of the radioguide catheter until the source wire""s radiation source reaches the vessel region to be treated. The radiation source is held in this region for a prescribed time duration, calculated to deliver an effective dosage of radiation. After irradiating the region, the source wire is withdrawn back into the afterloader.
The length of the patient""s stenosis to be treated can vary widely, and thus a physician generally must have access to a wide selection of source wires and radiation sources to treat any length stenosis. As was more generally discussed above, maintaining such a selection can be quite expensive.
The required selection of source wires can be limited by simulating a radiation source of a preferred length using a radiation source of much shorter length. In particular, a relatively short radiation source can be sequentially positioned at a plurality of locations along the treatment location in the patient""s body, to simulate a preferred length. This treatment method, however, can require a substantially longer period of time to complete. In particular, the radiation source must be positioned at each of a plurality of locations for roughly the same period of time that the preferred-length radiation source would be positioned at a single location in the body. This increased duration can cause both additional expense in general intervention costs, and additional risk of harm due to prolonged vessel obstruction.
In addition to length, arteries to be treated vary greatly in diameter, with typical values ranging from 2.0 mm to 4.0 mm. Since the radiation delivered by IRT sources drops rapidly with distance from the source, this variation in diameter causes the dose rate in a 2.0 mm diameter artery to be much higher than the dose rate for the same source treating a 4.0 mm diameter artery. This wide variation in dose rate has the potential to impact the efficacy of the IRT therapy.
Moreover, the dose rate must be controlled so as not to exceed safe levels of radiation delivered to the patient. There could be a negative effect if the dose rate is too high for a particular vessel region.
It should therefore be appreciated that a definite need has existed for a device to irradiate patients having a variety of treatment requirements, without requiring the expense of maintaining a selection of radioactive source wires having radiation sources of different lengths and activities, and without requiring the risks involved in frequently changing from one source wire to another. The present invention satisfies these and other needs, and provides further related advantages.
The present invention provides a medical catheter assembly and a related method of using the catheter assembly. A catheter assembly of the invention modifies the effective radioactive configuration of a radiation source when the radiation source is positioned within a patient""s body. The catheter assembly includes a catheter to be inserted into the patient""s body. The catheter defines a lumen configured to receive and position the radiation source within the patient""s body.
A catheter assembly of the invention includes a means for modifying the effective radioactive configuration of the positioned radiation source. The modifying means defines a treatment region. More particularly, this modifying means may be a radiation shield shielding a portion of the lumen. The radiation shield is configured and located to define the treatment region, modifying the effective radioactive configuration of the radiation source when it is positioned within the patient""s body.
A method of irradiating a portion of a patient""s body with a radiation source includes inserting a medical catheter assembly into the patient""s body. The catheter assembly includes a catheter defining a lumen and a radiation shield. The method can also include positioning the radiation source into the catheter""s lumen such that the radiation shield shields a portion of the body from the positioned radiation source.
Other features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrates, by way of example, the principals of the invention.